Ultrastructural localization of calcium deposits during in vitro culture of pig oocytes

Calcium deposits were localized using the combined oxalate–pyroantimonate technique in follicle‐enclosed oocytes fixed in situ. These deposits can be observed within vacuoles, mitochondria, and on the surface of yolk granules as well as in the caryoplasm, but are absent from the endoplasmic reticulum. Isolation of the oocyte from the follicle resulted in the immediate depletion of these calcium deposits. Replenishment of these deposits started during the first 8 hr of in vitro culture of the oocyte and they were gradually replenished to the levels observed before the liberation of oocytes during in vitro maturation to the stage of metaphase II. Mol. Reprod. Dev. 58:196–204, 2001. © 2001 Wiley‐Liss, Inc.